This invention relates to pulsed laser-deposited highly oriented yttria stabilized zirconia thin films fabricated on a plurality of substrate types.
Currently there is a great interest in the growth of highly oriented yttria stabilized zirconia (YSZ) films with specific electrical, mechanical, and optical properties. Oriented YSZ film applications range from dielectric buffer layers for yttria barium copper oxide (YBCO) superconductors to hard films used for wear protection in tribological (abrasion resistant) pairs. Laser ablation is one of the few YSZ deposition methods providing technological and economical solutions for growing the desirable  less than 001 greater than  oriented cubic and tetragonal YSZ films on polycrystalline substrates.
The growth of YSZ films by pulsed laser deposition (PLD) is currently typically accomplished in an oxygen background of 10xe2x88x924 to 10xe2x88x922 mbar pressure range, while the substrate temperature is maintained at about 800xc2x0 C. These conditions cause a thermally driven oxidation for the growth of stoichiometrically correct,  less than 001 greater than  equi-axial and in-plane oriented films. The background gas not only affects the chemistry on the substrate condensation surface, but also determines the chemistry and energetics within the ablation plume itself.
The fabrication of YSZ films is thus known in the art however in the past these films have been formed at temperatures requiring the use of non organic substrate materials; moreover these substrate materials are often required to be of a specific crystal orientation if a particular crystal orientation is desired in the fabricated film material. Similarly it is known in the art to employ a bias voltage on the substrate used to support a ceramic film during film fabrication, such bias voltages are however frequently used in a sputtering film-forming environment rather than in an ablation film-forming environment. Similarly the use of argon gas in forming a ceramic film is known in the art, however such gas is often seen in the form of ions in a beam rather than as a significant gaseous component in a laser ablation atmosphere. It is also known to employ ion bombardment in the fabrication of a ceramic film; such bombardment is however most commonly accomplished through use of an ion beam apparatus rather than through the laser ablation espoused in the present invention. Several aspects relating to the present invention are therefore known in their own right in the ceramic film art; the present invention however is believed to represent a new and particularly useful combination of such aspects and thereby to result in an advancement of the ceramic film art.
The present invention provides [001] oriented yttria stabilized zirconia films achieved at low temperature and in an ion beam-free processing sequence.
It is an object of the present invention therefore to provide a relatively low temperature process for achieving yttria stabilized zirconia films.
It is another object of the present invention therefore to provide a relatively low temperature process for achieving highly oriented yttria stabilized zirconia films.
It is another object of the present invention to provide an ion beam-free low temperature accelerated ion process for achieving yttria stabilized zirconia and related films.
It is another object of the present invention to provide an ion beam-free, low temperature, accelerated ion process for achieving yttria stabilized zirconia and related films.
It is another object of the present invention to provide a ceramic film-related ablation process operable with continuous direct current electrical energy.
It is another object of the present invention to provide a ceramic film-related ablation process operable with pulsating direct current electrical energy.
It is another object of the present invention to provide an improved yttria stabilized zirconia film fabrication process based on an enhanced degree of plasma diagnosis relevant to a laser ablation process.
It is another object of the present invention to provide an improved yttria stabilized zirconia film fabrication process based on a desirable degree of plasma formation achieved in a particular formation atmosphere.
It is another object of the present invention to provide an improved yttria stabilized zirconia film achieved through use of newly recognized advantageous combinations of film formation atmosphere composition, atmospheric pressure and atmospheric temperature.
It is another object of the present invention to provide an improved yttria stabilized zirconia film achieved through the use of advantageous combinations of argon and other gases in the film-formation atmosphere.
It is another object of the present invention to provide an improved yttria stabilized zirconia film achievable within realistic practical processing times.
It is another object of the present invention to provide an improved yttria stabilized zirconia film achieved with the use of random oriented yttria stabilized zirconia as an ablation material.
It is another object of the present invention to provide an improved yttria stabilized zirconia film achieved with the use of commercially available polycrystalline yttria stabilized zirconia as an ablated material.
It is another object of the present invention to provide an improved yttria stabilized zirconia film formable on a large variety of substrate materials, materials inclusive of metals, ceramics, plastics and low temperature compositions.
It is another object of the present invention to provide an improved yttria stabilized zirconia film formable on substrate materials of any Miller indices surface orientation, including random and amorphous surfaces.
It is another object of the present invention to utilize the advantages of an inclined substrate for receiving the forming yttria stabilized zirconia film.
Additional objects and features of the invention will be understood from the following description and claims and the accompanying drawings.
These and other objects of the invention are achieved by the method of forming oriented yttria stabilized zirconia films comprising the steps of:
disposing a target source of polycrystalline yttria stabilized zirconia in a closed atmosphere of selected gaseous composition, flow rate, temperature and pressure;
locating a film-receiver substrate of selected composition in said closed atmosphere of selected gaseous composition, temperature and pressure;
ablating a segregated plume of zirconium ions and remainder plasma from a surface portion of said polycrystalline yttria stabilized zirconia target source using energy emissions from a laser of selected operational characteristics;
said substrate being disposed in a selected angular orientation with respect to a straight line path joining said substrate and said target source of polycrystalline yttria stabilized zirconia;
attracting said zirconium ions and said remainder plasma toward said substrate by lowering said substrate in electrical potential below that of said polycrystalline yttria stabilized zirconia target source.